Method for bulk curing tobacco



N V-12; 1963 F. J. HASSLER 3,110,326

METHOD FOR BULK CURING TOBACCO Original Filed June 13, 1960 2 Sheets-Sheet J.

[Q] 3w- 2% sec. INVENTOR.

JIEZ

Nov. 12, 1963 F. J. HASSLER 3,110,325

METHOD FOR BULK CURING TOBACCO Original F iled June 13. 1960 2 Sheets-Sheet 2 INVENTOR. FRANCIS J. l/flSSlE'Z H15 4 TTOENEYS United States Patent vided and this application Oct. 9, 1961, Ser. No. 143,635

3 Claims. (Cl. 13114il) The present invention relates to an improved method for curing tobacco and, more particularly, to a method for curing tobacco in bulk; however, the invention is not necessarily so limited.

The present application is a division of my copending application Serial No. 35,499, filed June 13, 1960, for Method and Apparatus for Bulk Curing Tobacco.

A fundamental problem in tobacco production is the great amount of hand labor required in the conventional method of production. Approximately three-fourths of the total labor required in the production of tobacco is devoted to harvesting and processing operations. In recent years much has been done in the way of mechanizing harvesting operations, and the labor saving through mechanization has been substantial. However, there has been little advance in the techniques for processing the harvested tobacco. Thus, the techniques for processing tobacco today are, with the exception of a few minor improvements, the same as employed more than a century ago.

In curing tobacco it has long been the practice to string the tobacco leaves on elongated sticks which are supported in a curing barn. The stringing operation is a cumbersome and time consuming operation which must be done by hand. When the tobacco has been strung and placed in the barn, it is carried through a curing operation which can be roughly divided into four stages.

These stages will be described in detail in the following remarks. Accordingly, it suflices for the present to state that the first stage is a leaf yellowing stage wherein physiological transformations evidenced by yellowing of the tobacco leaf occur. dehydrated to halt the physiological transformations occurring in the leaf. In the third stage the dehydration is accelerated so that the stem of the tobacco leaf is dried out. At this point, the tobacco leaf is substantially bone dry and the leaf itself is very fragile. In the final stage moisture is added to the leaf so that it softens and can be handled. Thereafter, the tobacco is ready for removal from the curing barn for subsequent processing.

It is obvious that the curing of tobacco could be greatly simplified if it were possible to cure the tobacco in bulk. This would eliminate the cumbersome stringing operation since it would then be possible to cure the tobacco in large bundles. Unfortunately, however, the leaf yellowing stage described above involves exothermic reactions in the tobacco leaf. Thus, when tobacco is cured in bundles, large amounts of heat must be dissipated. For this reason, it has been considered impossible to satisfactorily control a bulk curing operation.

It is an object of the present invention to provide a method for curing tobacco which enables bulk curing and which afi'ords suflicient control over the curing process that the heat released exotherrnioally does not impair the operation.

Still another object of this invention is to provide an improved method for bulking tobacco in racks.

Otherobjects and advantages reside in the construction of parts, the combination thereof, the method of manufacture and the mode of operation, as will become more apparent from the following description.

FIGURE 1 is a perspective view of the tobacco curing barn.

In the second stage the leaf is 3,1 10,326 Patented Nov. 12, 1963 FIGURE 2 is an end elevational view of the barn taken from the direction indicated by the arrows 22 of FIG- URE 1.

FIGURE 3 is a sectional view of the barn taken substantially along the lines 3-3 of FIGURE 1.

FIGURE 4 is a plan view of the interior of the barn.

FIGURE 5 is a longitudinal sectional view of the barn illustrating heating apparatus employed therein.

FIGURE 6 is a perspective view illustrating the method of placing tobacco leaves in a rack.

FIGURE 7 is a perspective view illustrating a completed rack of tobacco.

FIGURE 8 is a fragmentary plan view of an assembled rack with the tobacco removed.

FIGURE 9 is an end view taken in the direction of the arrows 99 of FIGURE 8.

Referring to the drawings in greater detail, FIGURE 1 illustrates a tobacco barn 10 which is designed specifically for use in the present method. The exterior covering for the barn is formed with a plurality of arched sheet metal panels 11. At the forward end of the barn, as viewed in FIGURE 1, an overhang 12 is provided. This overhang provides a shelter where tobacco leaves may be placed in racks, as will be described hereinafter, prior to movement into the curing barn.

Behind the overhang 12 is a partition 14 which closes the forward end of the barn. As best illustrated in FIG- URE 2, this partition includes three doors 14a, 14b and which may be opened to gain access to three separate compartments within the barn.

Rearward of the partition 14 is another partition 16 which cooperates with a rear end wall 18 to establish a furnace room. The partition 16 isolates the furnace room from the central part of the barn.

As best seen in FIGURE 3, the central part of the barn is divided into three sections by a pair of dividers 20a and 20b extending between 1he partitions 14 and 16. The doors 14a and 14b and 140 open separately into these sections.

The dividers 20a and 2%, as well as the side walls of the barn, support horizontal rails 22 which form supporting shelves for tobacco racks placed thereon. FIGURE 3 schematically illustrates tobacco racks or supporting frames 24 supporting tobacco leaves 26 mounted on the rails 22. In the tobacco barn illustrated, two tiers of tobacco racks are placed in each of the three sections of the barn.

FIGURES 4 and 5 illustrate a heating system which is installed in the barn. This system includes a furnace 30 located in the furnace room between the partition 16 and the end wall 18. Leading from the furnace at floor level are three outlet ducts 36a, 36b and 360, each of which is regulated by a hand damper 34. These three ducts pass centrally through the three sections of the central portion of the barn and are each provided with a plurality of spaced openings or ports 38 in the sides thereof through which air may escape. A blower unit 32 located the furnace forces air into the duct 36. The leaving the ports 3t; moves upwardly between the bulked tobacco leaves and ultimately flows into a return duct 44} located centrally in the barn at an elevation above the dividers 20a and 2011. This duct 40 is provided with spaced ports 42 into which the m'r moves.

A damper 44 is located in the duct 40 between the several ports 42 and the blower 32. Above the damper is an outlet duct 46, best seen in FIGURE 4, communieating with the outside atmosphere. By adjustment of the damper 44, varying amounts of fresh air may be admitted to the heating system, or if desired, the duct 46 may be closed such that the air within the system is recirculated without addition of fresh air.

The blower 32 operates to establish a pressure differen- 'escape of air around the ends of the racks.

=2 tial between the top and bottom of the curing barn in the central curing section such that the air is forced to move upwardly through the tobacco. The design of the racks is such as to force the circulated air to flow between the bulked tobacco leaves.

An individual rack 24 is illustrated in FiGURES 8 and 9. This rack includes an elongate side member 50 with outwardly extending rods 52.. fixedly secured to each end thereof. A second side member 54 of equal length has apertures 53 therein complementary to the rods 52, the arrangement being such that the rods 52 may be projected into the apertures 53 to assemble the rack. Suitable nuts 55 are threaded onto the rods 52 to fix the assembly. The side member 54 carries a plurality of parallel fixedly attached spikes 56 which, in the assembled rack, abut a shoulder 58 provided on the side member 50.

In bulking tobacco, the rack is used in association with a bin 60 illustrated in FIGURE 6. This bin has an open top and one open side. The end walls 62. of the bin are hingedly joined to the rear panel 63 and are normally locked in the position illustrated in solid line detail. In inserting the tobacco into the rack, the side member 50 is seated on the bottom of the bin and is located by slots 64 provided in the end walls 62. The rods 52. carried by the side member '0 project upwardly in the slots 64.

The bin 6% is then filled :wit'n tobacco leaves each of which has its base butted against the rear panel 63. The side member 54 is then pressed downwardly into the bin 60 to force the spikes 56 through the tobacco leaves. Any suitably designed press mechanism may be employed to force the side member 54 into the bin 60 in accurate registry with the side member 50.

After the side member 54 has been forced into the bin 60 and secured by means of nuts 55 engaging the rods 52, the end walls 62 are swung outwardly so that the rack may be removed from the bin. A completed rack of tobacco is illustrated in FIGURE 7. In the completed rack, the shoulder 58 provided on the side member 50 supports the ends of the spikes 56 so that the weight of the tobacco does not deform the spikes.

In loading the racks in the curing barn the racks are slid along the rails 22 and pushed one after the other into the barn. The dimensions of the racks are modular with respect to the interior of the barn so that when a full complement of racks are butted one against the other, they exactly fit between the partitions 14 and 16 leaving substantially no room for escape of air around the sides of the racks. In this regard it will be noted in FIGURE 3 that the leaves of the tobacco flare outwardly from the racks and cooperate with the rails 22 to minimize the The air which is forced upwardly through the central portion of the barn must therefore move in and around the tobacco leaves.

As mentioned hereinbefore, the initial portion of the tobacco curing cycle involves exothermic reactions and it is important that the temperature of the tobacco leaves be carefully controlled during this portion of the cycle. This is done by forcing air of the correct temperature and humidity through the tobacco.

At the beginning of the curing process, the tobacco leaf has a green coloration due to the presence of chlorophyll therein and additionally contains complex starch and protein molecules, nicotine, water and many other components. The leaf moisture content is normally 80 to 90 percent of the total green weight of the leaf. In the initial curing stage, designated the leaf yellowing stage, the major chemical conversions are the simplification of complex starch and protein molecules and the disappearance of chlorophyll by oxidation. Rapid desiccation at this stage would arrest all chemical conversions and accordingly the moisture con-tent of the leaves must be maintained above 70 percent. This is not meant to imply that all chemical action of any sort ceases when the leaf moisture content drops below 70 percent. Rather, when the 4- leaf moisture content has reached this low level, it is found that chemical action proceeds at such a low rate that further visible changes in the leaf do not occur. During the initial curing stage, starch molecules are hydrolyzed to simpler sugars. The disappearance of chlorophyll proceeds at a rate parallel to the conversion of starch. Thus, the leaf color is a good indication of the state of the leaf. When all chlorophyll has disappeared the major portion of the starch has been hydrolyzed. This is evidenced by a yellowing of the leaf as the disappearing chlorophyll unmasks yellow leaf pigments.

The rate at which the aforementioned reactions occur increases with an increase in temperature. Hence, the cure time is shortened with increasing temperature. However, when the temperature exceeds 110 R, an undesirable browning resulting from oxidation of polyphenols occurs, along with other reactions which result in an accumulation of undesirable components. Under the circumstances it is found preferable to control the leaf temperature to around 100 F. This is accomplished by circulating air which has a temperature in the range to F. through the tobacco. During this stage of the cure a relative humidity of 85 to 95 percent is employed. The dampers are therefore set to allow a high humidity.

The yellowing stage is normally accomplished within 30 to 60 hours depending upon the state of the leaves when the cure is begun. During this period, the moisture content of the leaf is reduced to about 70 to 75 percent.

After yellowing is accomplished, that is, after the leaf is at the desired chemical state, further chemical reaction is arrested by dehydrating the leaf. This stage of the cure process is known as the leaf drying stage. To accomplish dehydration, the air temperature is elevated at a rate of 2 to 3 F. per hour and is ultimately held in the range of to F. To insure maximum desiccation, the dampers are adjusted to exhaust the humid air with no recirculation. The normal time required for the leaf drying stage is from 20 to 30 hours during which the leaf moisture content is reduced to a level of 30 to 50 percent. With avenage atmospheric conditions the air circulated through the curing barn during this stage has a relative humidity of around 40 percent.

After dehydration of the leaf, the cure is carried into a stem drying stage wherein moisture is extracted from the midribs. In this stage the temperature is increased at the rate of 2 to 5 F. per hour to to F. During this stage the dampers are set to achieve 90 to 100 percent recirculation of air, thus conserving on fuel. After 15 to 30 hours of drying under these conditions the stems become brittle while the moisture content of the leaf lamina approaches zero. The leaf becomes crisp and fragile in this stage and it is necessary to recondition or reorder the leaf before removal from the curing barn.

In the final stage of the tobacco cure, moisture is added to the leaf. This may be accomplished in two Ways. Under favorable environmental conditions of 50 to 70 F. and 85 to 100 percent relative humidity, air can be drawn in from outside the barn and forced through the tobacco without additional heat, then exhausted from the barn. However, when the ambient atmosphere is not sufficiently humid it is found preferable to employ a humidifier, not shown, located Within the duct work. The controls are set to provide a temperature of from 80 to 100 F. and a relative humidity of around 85 percent with full recirculation of air. Normally the leaf is conditioned to a moisture content of 15 to 20 percent by weight. The time required for this. reconditioning is 6 to 10 hours. The tobacco is then ready for removal from the curing barn.

It is found that bulk curing on the cycle indicated produces a marketable tobacco leaf comparable to the best obtained with conventional curing techniques. At the same time, it is found that the cure obtained is more uniform than that obtained conventionally such that a higher average market price is realized. Another important advantage resulting from the method and apparatus disclosed herein is a substantial reduction in the amount of labor required to elfect the cure.

Although the preferred embodiment of this method has been described, it will be understood that within the purview of this invention various changes may be made in the form, details, proportion and arrangement of parts, the combination thereof, the method of manufacture and mode of operation, which generally stated consist in a device capable of carrying out the objects set forth, as disclosed and defined in the appended claims.

Having thus described my invention, I claim:

1. A method of curing green tobacco leaves which comprises the steps of assembling a multiplicity of green tobacco leaves together into loose bulk form with the flat surfaces thereof extending generally in the same direction and a substantial portion of the flat surfaces in parallel relation, compacting and peripherally confining the assembled leaves into a compact bulk bundle, providing interior support within the peripheral confinement at spaced positions through substantially all of the leaves of the compact bulk bundle intermediate the ends of said leaves, supporting a plurality of said compact bulk bundles within a confined zone solely by the peripheral confinements thereof with the latter disposed generally horizontally and the that surfaces of the leaves disposed generally vertically at positions such that a flow of forced air within said confined zone will pass only between the fiat surfaces of the leaves within the peripheral confinements thereof, establishing a substantially continuous flow of forced air vertically between the fiat surfaces of the leaves of said plurality of compact bulk bundles within the peripheral confinements thereof While said plurality of bulk bundles are supported within said confined zone for a first time period at a temperature less than 110 F. while controlling the relative humidity of the air sufllcient to maintain a relatively high moisture content level in the leaves so that substantially all of the chlorophenyll in the tobacco leaves is oxidized unmasking the yellow pigments present in the leaves, substantially continuously maintaining a forced flow of air while maintaining said support of the plurality of bulk bundles within said confined zone for a second time period at a temperature which is gradually increased and held at an intermediate elevated level while controlling the relative humidity of the air suflicient to initially arrest the chemical action taking place at the end of the first time period and to dehydrate the leaves to an intermediate lower moisture content level at the end of the second time period, substantially continuously maintaining a forced flow of air while maintaining said support of the plurality of the bulk bundles Within said confined zone for a third time period at a temperature which is gradually increased and held at an upper elevated level while controlling the relative humidity of the air sufiicient to bring the leaves to a crisp and fragile condition at the end of the third time period, and substantially continuously maintaining a forced flow of air whi'lemaintaining said support of the plurality of bulk bundles within said confined zone for a fourth time period at a reduced temperature level while controlling the relative humidity of the air sufficient to provide the leaves with a final moisture content permitting them to be handled without substantial breakage.

2. A method as defined in claim 1 wherein said relatively high moisture content level is in the range of about -75% by weight, said intermediate lower moisture content level is in the range of about 30-50% by weight, and said final moisture content is in the range of about 15-20% by weight, and wherein said intermediate elevated temperature level is in the range of about F., said upper elevated temperature level is in the range of about -170 F., and said reduced temperature level is in the range of about 80-100 F.

3. A method as defined in claim 1 wherein said plurality of compact bulk bundles are supported within said confined zone in a pair of vertically spaced tiers, each tier including a plurality of horizontally aligned compact bulk bundles disposed with respect to each other so as to prevent passage of air therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 10,750 Lafetra Apr. 4, 1854 123,760 Ashcroft Feb. 20, 1872 553,723 Proctor Ian. 28, 1896 918,075 Muggli Apr. 13, 1909 1,545,811 Buensod Nov. 21, 1924 1,555,779 Vietor Sept. 29, 1925 1,568,316 Buensod Jan. 5, 1926 2,016,535 Bogaty Oct. 8, 1935 2,475,568 Moore July 5, 1949 2,989,057 Touton June 20, 1961 OTHER REFERENCES The Production of Tobacco, by W. W. Garner, pages 399, 405, 406, 407. Pub. 1951 by The Blakiston Co., Phila., Pa.

The Production of Tobacco, by W. W. Garner, pub. 1951 by The Blakiston Co., Phila, Pa.

Research and Farming, pages 8 and 9, publication of North Carolina State College, vol. XV, No. 4 (Spring 1957), article by Johnson et 'al., entitled Barnless Curln gja Tobacco Science, vol. 2, pages 23-28, Mar. 14, 1958, article by Henson et al., entitled Yellowing Flue Cured Tobacco in Bulk.

Raleigh News and Observer, Nov. 10, 1958, page 15, article entitled Bulk Leaf Curing Method Ready for Farm Testing, by Tom Byrd.

Tobacco, vol. 150, No. 12, Mar. 18, 1960 issue, pages 22-28. Article entitled Bulk Curing of Bright Leaf Tobacco, by W. H. Johnson, W. H. Henson, F. J. Hassler and W, W. Watkins. 

1. A METHOD OF CURING GREEN TOBACCO LEAVES WHICH COMPRISES THE STEPS OF ASSEMBLING A MULTIPLICITY OF GREEN TOBACCO LEAVES TOGETHER INTO LOOSE BULK FORM WITH THE FLAT SURFACES THEREOF EXTENDING GENERALLY IN THE SAME DIRECTION AND A SUBSTANTIAL PORTION OF THE FLAT SURFACES IN PARALLEL RELATION, COMPACTING AND PERIPHERALLY CONFINING THE ASSEMBLED LEAVES INTO A COMPACT BULK BUNDLE, PROVIDING INTERIOR SUPPORT WITHIN THE PERIPHERAL CONFINEMENT AT SPACED POSITIONS THROUGH SUBSTANTIALLY ALL OF THE LEAVES OF THE COMPACT BULK BUNDLE INTERMEDIATE THE ENDS OF SAID LEAVES, SUPPORTING A PLURALITY OF SAID COMPACT BULK BUNDLES WITHIN A CONFINED ZONE SOLELY BY THE PERIPHERAL CONFINEMENTS THEREOF WITH THE LATTER DISPOSED GENERALLY HORIZONTALLY AND THE FLAT SURFACES OF THE LEAVES DISPOSED GENERALLY VERTICALLY AT POSITIONS SUCH THAT A FLOW OF FORCED AIR WITHIN SAID CONFINED ZONE WILL PASS ONLY BETWEEN THE FLAT SURFACES OF THE LEAVES WITHIN THE PERIPHERAL CONFINEMENTS THEREOF, ESTABLISHING A SUBSTANTIALLY CONTINUOUS FLOW OF FORCED AIR VERTICALLY BETWEEN THE FLAT SURFACES OF THE LEAVES OF SAID PLURALITY OF COMPACT BULK BUNDLES WITHIN THE PERIPHERAL CONFINEMENTS THEREOF WHILE SAID PLURALITY OF BULK BUNDLES ARE SUPPORTED WITHIN SAID CONFINED ZONE FOR A FIRST TIME PERIOD AT A TEMPERATURE LESS THAN 110* F. WHILE CONTROLLING THE RELATIVE HUMIDITY OF THE AIR SUFFICIENT TO MAINTAIN A RELATIVELY HIGH MOISTURE CONTENT LEVEL IN THE LEAVES SO THAT SUBSTANTIALLY ALL OF THE CHLOROPHENYLL IN THE TOBACCO LEAVES IS OXIDIZED UNMASKING THE YELLOW PIGMENTS PRESENT IN THE LEAVES, SUBSTANTIALLY CONTINUOUSLY MAINTAINING A FORCED FLOW OF AIR WHILE MAINTAINING SAID SUPPORT OF THE PLURALITY OF BULK BUNDLES WITHIN SAID CONFINED ZONE FOR A SECOND TIME PERIOD AT A TEMPERATURE WHICH IS GRADUALLY INCREASED AND HELD AT AN INTERMEDIATE ELEVATED LEVEL WHILE CONTROLLING THE RELATIVE HUMIDITY OF THE AIR SUFFICIENT TO INITIALLY ARREST THE CHEMICAL ACTION TAKING PLACE AT THE END OF THE FIRST TIME PERIOD AND TO DEHYDRATE THE LEAVES TO AN INTERMEDIATE LOWER MOISTURE CONTENT LEVEL AT THE END OF THE SECOND TIME PERIOD, SUBSTANTIALLY CONTINUOUSLY MAINTAINING A FORCED FLOW OF AIR WHILE MAINTAINING SAID SUPPORT OF THE PLURALITY OF THE BULK BUNDLES WITHIN SAID CONFINED ZONE FOR A THIRD TIME PERIOD AT A TEMPERATURE WHICH IS GRADUALLY INCREASED AND HELD AT AN UPPER ELEVATED LEVEL WHILE CONTROLLING THE RELATIVE HUMIDITY OF THE AIR SUFFICIENT TO BRING THE LEAVES TO A CRISP AND FRAGILE CONDITION AT THE END OF THE THIRD TIME PERIOD, AND SUBSTANTIALLY CONTINUOUSLY MAINTAINING A FORCED FLOW OF AIR WHILE MAINTAINING SAID SUPPORT OF THE PLURALITY OF BULK BUNDLES WITHIN SAID CONFINED ZONE FOR A FOURTH TIME PERIOD AT A REDUCED TEMPERATURE LEVEL WHILE CONTROLLING THE RELATIVE HUMIDITY OF THE AIR SUFFICIENT TO PROVIDE THE LEAVES WITH A FINAL MOISTURE CONTENT PERMITTING THEM TO BE HANDLED WITHOUT SUBSTANTIAL BREAKAGE. 